package main

import "fmt"

func main() {
	var a int
	m := make(map[int]bool, 10)
	for i := 0; i < 9; i++ {
		fmt.Scan(&a)
		m[a] = true
	}
	for i := 1; i <= 10; i++ {
		if !m[i] {
			fmt.Println(i)
			return
		}
	}
}